1. Field of the Invention
The present invention relates to a solid-state imaging device having a function of clamping, referring to a readout signal level in an optical black region, a signal in a valid pixel region with a value with which the signal level is reduced to zero.
2. Description of the Related Art
As a technique for correcting deterioration in image quality due to dark current, as disclosed in, for example, JP-A-2004-80168, there is a technique for clamping, referring to a readout signal level in an optical black region, a signal in a valid pixel region with a value with which the signal level is reduced to zero.
As one of systems for realizing such a technique, there is known a feedback control system for calculating, from a readout signal level in an optical black region of the present frame, a clamp value with which the signal level is reduced to zero and setting the clamp value as a clamp value in reading out the next frame.
In the feedback control system, in order to suppress oscillation of a clamp control amount, feedback is performed at a feedback ratio smaller than one. Therefore, time for a period of several frames is necessary until convergence of the clamp value.
There is also known a driving system for combining plural frames having different accumulation times to expand a dynamic range.
In the driving system, a clamp value is stored for each of the frames having the different accumulation times to perform feedback control for a clamp amount.